1. Field of the Invention
Embodiments of the present invention relate to a wireless power transmission method and apparatus for improving spectrum efficiency and space efficiency based on impedance matching and relay resonance.
2. Description of the Related Art
Technology for wirelessly transmitting energy through mutual resonance based on magnetic resonance was proposed by the Massachusetts Institute of Technology (MIT) in 2007. The proposed technology involves a helical structure and a resonant frequency of 10 megahertz (MHz). A structural size of a helical resonator is approximately 600 millimeters (mm) in diameter, and has 5.25 helical turns. A line thickness is approximately 6 mm in diameter, and a total helical thickness is approximately 200 mm. A single signal feeding roof is approximately 250 mm. Here, an issue of splitting of resonant frequencies of resonators may occur as magnetic resonators become closer to one another. Thus, an issue of a resonant frequency differing from an initial resonant frequency may arise. Such a physical issue may occur in general resonant structures. Such a resonant frequency shift issue may result in inconvenience, requiring a resonant frequency tracking operation.
Also, the technology for wirelessly transmitting energy may be used for more diverse applications when a size of a receiving resonator is smaller. However, the smaller the size of the receiving resonator, the smaller a power transmission distance. Thus, the small-sized receiving resonator may have a spatial limitation. For example, when the receiving resonator has a diameter of R, designing and manufacturing the receiving resonator to have a transmission distance with a radio frequency (RF) efficiency of 80% or higher that may satisfy the diameter R of the receiving resonator may be challenging. Although such a small-sized resonator may be developed, the transmission distance may be limited to the diameter of the resonator. In general, wireless power transmission technology based on magnetic resonance may have a characteristic of mid-distance transmission with the transmission distance of approximately 1 meter (m). In general, the diameter of the resonator may be considered a limitation to the transmission distance. Accordingly, technology for expanding the transmission distance may be required.